remove everything related to forkall

i made a best attempt, but the intended semantics of this function are
fundamentally contradictory. there is no consistent way to handle
ownership of locks when forking a multi-threaded process. the code
could have worked by accident for programs that only used normal
mutexes and nothing else (since they don't actually store or care
about their owner), but that's about it. broken-by-design interfaces
that aren't even in glibc (only solaris) don't belong in musl.

include/unistd.h

@@ -168,7 +168,6 @@ char *getusershell(void);
 #endif
 
 #ifdef _GNU_SOURCE
-pid_t forkall(void);
 int setresuid(uid_t, uid_t, uid_t);
 int setresgid(gid_t, gid_t, gid_t);
 int getresuid(uid_t *, uid_t *, uid_t *);

src/internal/libc.h

@@ -52,7 +52,6 @@ void __unlockfile(FILE *);
 #define UNLOCK(x) (libc.threads_minus_1 ? (__unlock(x),1) : ((void)(x),1))
 
 void __synccall(void (*)(void *), void *);
-void __synccall_wait(void);
 int __setxid(int, int, int, int);
 
 extern char **__environ;

src/thread/forkall.c

@@ -1,68 +0,0 @@
-#if 0
-#include "pthread_impl.h"
-#include <setjmp.h>
-
-struct thread {
-	struct thread *next;
-	pthread_t td;
-	jmp_buf jb;
-	void *tmp, *stack;
-};
-
-struct ctx {
-	struct thread *list;
-	pthread_t caller;
-	pid_t pid;
-	size_t cnt;
-	pthread_barrier_t barrier;
-};
-
-static void restart_thread(pthread_t self)
-{
-	struct thread *t = self->start_arg;
-	self->start_arg = t->tmp;
-	self->pid = getpid();
-	longjmp(t->jb, 1);
-}
-
-static void do_forkall(void *p)
-{
-	struct ctx *c = p, *volatile cv = c;
-	char tmpstack[2048];
-	struct thread *tp, t = {
-		.td = __pthread_self(),
-		.next = c->list,
-		.stack = tmpstack+1024
-	};
-
-	if (t.td != c->caller) {
-		c->cnt++;
-		t.tmp = t.td->start_arg;
-		t.td->start_arg = &t;
-		if (setjmp(t.jb)) {
-			c = cv;
-			if (c->pid) return;
-			pthread_barrier_wait(&c->barrier);
-			return;
-		}
-		c->list = &t;
-		__synccall_wait();
-		return;
-	}
-	c->pid = syscall(SYS_fork);
-	if (c->pid) return;
-
-	pthread_barrier_init(&c->barrier, 0, c->cnt);
-	for (tp=c->list; tp; tp=tp->next)
-		if (__uniclone(tp->stack, restart_thread, tp->td) < 0)
-			_exit(127);
-	pthread_barrier_wait(&c->barrier);
-}
-
-pid_t forkall()
-{
-	struct ctx c = { .caller = pthread_self() };
-	__synccall(do_forkall, &c);
-	return c.pid;
-}
-#endif

src/thread/synccall.c

@@ -47,14 +47,6 @@ static void handler(int sig, siginfo_t *si, void *ctx)
 	errno = old_errno;
 }
 
-void __synccall_wait()
-{
-	struct chain *ch = cur;
-	sem_post(&ch->sem2);
-	while (sem_wait(&ch->sem));
-	sem_post(&ch->sem);
-}
-
 void __synccall(void (*func)(void *), void *ctx)
 {
 	pthread_t self;